The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
To reduce weight and increase strength in power-train components such as hypoid differential assemblies, laser welding has been utilized to join various components together such as carburized steel hypoid ring gears and nodular iron differential cases.
Concerns in the art of welding nodular iron to steel are known and typically a joined weld pool should have a carbon content below 1.2 weight percent (wt %.) to prevent weld failures. Manufacturers attempt to reduce the carbon content by removing the carburized layer from the hypoid ring gear thru machining or utilizing carbon blocking pastes or physical alloy caps in the heat treatment process to prevent carbon from diffusing into the steel. Machining hardened steel components involves both a high machining time and low tool life.
These methods have inherent issues such as variability in the blocking of carbon diffusion, which leaves hard zones unknown to the subsequent hard machining operations. The variability in the blocking of carbon diffusion is also an area of potential weld failure if the carbon is insufficiently removed.
Further, tools used to machine the carburized surface are expensive and must be replaced regularly due to the large amount of wear from machining the carburized surface. The alloy caps used to prevent carbon from diffusing into the steel yield inconsistent results. These inconsistent results can cause tool failures when the tooling encounters the hardened portions. The carbon blocking pastes are messy, yield inconsistent results, and reduce the service life of furnace bricks and require additional exhaust procedures.
Typically, when the material hardness Rockwell C scale (HRC) exceeds 50 (>50 HRC) hard machining is necessary to create the precise weld joint geometry and remove the total effective case back to the parent metal carbon content typically <0.25 wt %. Removal of the total effective case through machining (hard turning) is typically done with cubic boron nitride (CBN) tooling and requires multiple shallow cuts to remove material without catastrophic tool failure. The shallow depths of cut increase the cycle time, however, the tool life may still be inadequate.
The issues of increased cycle time, inadequate tool life, and other gear welding issues are addressed by the present disclosure.